Reed relay for small voltages



Oct. 17, 1961 F. w. slPPAcH ETAL 3,005,069

REED RELAY FOR SMALL. voLTAGEs Filed Jan. 27, 1961 E I INVENToRs y 3,605,069 I i yREED RELAY FOR SMALL voLTAGEs Frederick W. Sippach, Crafton Borough, and Robert'H..

Luppold, Jr., West Newton,-Pa.,'-assignors toI-Iagan Chemicals & Controls, Inc., Pittsburgh, .Pa. f

Filed Jan. 27, 1961, Ser; No. 85,313 5 Claims.v (Cl. 200e-87) 4 This invention relates to, electrical-relays. `In'particular, it relates to means for maintainingk equal temperatures atlthe terminals of magnetically activated reed relays.

The so-called reed relay has recently become eXtensively used in electrical devices requiring many switching operations because ofits low cost, long life, and minimumk contact contamination., The life expectancy of -a reed relay is `in the many millions of operations. 'Ilhe cost, on the other hand, is smallcompared to stand-` -ard mercury or. other types of relays. There is, however, a diiculty with freed relays which is especially troublesome when the relayishandling voltages in ythe microvolt ranges. This di'iculty is that the junctions of the leads and the terminals of the reeds are ordinarily unavoidably subject torsmall ditferencesin temperature. The reed contact strips, which are generally made of a ferrous alloy having a high nickel content, arey joined to the leads, which are generally of copper, at points several inches apart on the same relay. The junctions form thermocouples which produce yan in the neighborhood of 30 microvolts per degree centigrade of temperature difference. The generated by the thermocouplejunctions at each end of the relay is canceled out to the extent that there is no difference in the two temperatures. However, where there is a difference in temperature between the two lead-reed junctions of a single relay, the is quite significant. Where the relay is to be used to close -a circuit from a transducer having an output measured in microvolts, such as a thermocouple, for example, the error is likely to be as large as the analog signal. It is therefore imperative, if the reed relay is to be used for handling small voltages, that a means for compensating or correcting this error be provided.

We have invented a device for virtually equalizing the temperatures at the terminals of one or more reed relays. Our device also has the adv-antage of minimizing the error caused by thermocouple effects at the contact point where slight variations in alloy composition may be present in the reeds. An additional function of our device is that it provides an electrostatic shield between the coil and the capsule containing the reeds. Other advantages of the invention will be mentioned in the description and will in part be apparent to those skilled in the art to which the invention pertains.

Our invention is illustrated in its presently preferred forms in the accompanying drawings.

FIGURES la and lb are two views of a single presently commercially available reed relay capsule.

FIG. 2 is a cross section ofa single complete'reed relay equipped with our invention.

FIG. 3 is a perspective View of a presently preferred form of our thermal shunt capable of accommodating ytwo reed relays.

FIGS. 4a and 4b are an overhead sectional view and a cross section of a package of four relays, two of which are enclosed in the thermal shunt of our invention and two of which are outside the thermal shunt but within the insulated package.

Referring to FIG. l, it will be seen that the illustrated relay capsule comprises two metal strips 1 and 2 sealed in glass enclosure 3. i The strips are of ferromagnetic,

electrically "conductive metal, preferably a nickel-iron alloy having a coefficient of expansion approximately equal to that of theglass enclosure. Contact surfaces 4 are. gold-coated for improved conductance at the contact point. The interior 5 of the glass enclosure 3 is preferably filled with an inertv gas to minimize contact contamination and deterioration through corrosion, etc. The

space between contacts 4 is preferably about 2 or 3 mi1limeters. Each reed is securely anchored in the glass enclosureat 6. kApplication of a magnetic eld from the coil causes the reeds to assume a position parallel with the magnetic lines of force, thereby contacting each other.

The commercially available relay-.is not complete, of course., Without the energizing coil surrounding it.` The coil providedfor the unit described should have at least about 110 ampere turns per capsule to operate depend- Thermal shunt 44 next surrounds the relay. On this is placed vanother layer of insulating material 45. The energizing coil 46 is positioned concentrically on the insulating layer. The coil may, of course, be covered by a plastic insulating or protective layer 47.

FIG. 3 is va presently preferred form of our thermal shunt. This shunt is capable of accommodating two reed relays side by side. The material is one of high thermal conductivity but preferably also of relativelyk high specific heat; that is, it should be a good conductor f of heat and at the same time a given mass of material should absorb a relatively large number of calories for each degree of temperature change. A relatively large mass of such material in the form of our thermal shunt will result in a correspondingly high thermal inertia. However, the relay will not operate if the thermal shunt has ferromagnetic properties. excellent material with respect to thermal conductivity, specific heat, and cost, is copper. Copper is our presently preferred composition for the thermal shunt. Among other suitable materials may be mentioned silver and copper alloys having the above described characteristics.

FIG. 4a shows the use of our invention in a package of four relays. This is an overhead view illustrating relays lltl, 11, 12, and 13 of the type illustrated in FIG. l. Surrounding relays 11 and 12 is the thermal shunt 14 of FIG. 3. The other relays 10 and 13 are preferably positioned as shown, adjacent to the thermal shunt. Coil 17 surrounds the several relays such that energizing the coil 17 actuates all four relays at once. The entire package as shown is surrounded by a plastic protector. Insulating material 18 performs the important function of insulating the thermal shunt and the relay capsule within it from the relatively large temperature changes which occur in the coil. The insulating material should extend Ibeyond the ends of the reeds and seal off the ends of the package, as shown. By retarding the conduction of heat from the coil to the thermal shunt, the insulating material minimizes the effect of temperature change, resulting in minimal thermal gradients in the contact strips. The coil is preferably of ythe same shape as the shunt and equidistant from it on opposite sides.

The copper leads 19 are preferably as thin as possible in order yto minimize the conductance of heat through them to the ther-mocouple-like junctions 20, 21, 22, rand 23. It is these junctions, of course, which should be equalized so far yas is possible in temperature. Our invention provides a remarkably effective means for accomplishing this object.

The shunt should overhang the lead junctions to equalize the temperature so far as possible on all sides. In-

Patented Oct.. 17., 1961 We have found that any sul-ating material 18 should lill the space of the overhang to protect the junction from temperature inuences of the outside world.

The thermal shunt is placed lconcentrically between the coil and therelay or relays to be protected. Most of the heat changes which cause the thermal gradients at the ends of an ordinary relay originate with the energizing of the coil. The balance of the trouble comes lfrom the influence of air currents and the like originating outside the relay. The heat changes caused by the -coil and conducted to the ends of the relay are thus virtually equal. Indeed, the temperature changes throughout the length of the relay at the same rate. Compensation is therefore also made for any differences in alloy composition of the reeds resulting in a thermocouple effect at the contact surface.

It is to be distinctly understood that the embodiments of our invention illustrated and described herein are the presently preferred embodiments. Our invention may be otherwise variously practiced within the scope of the following claims.

We claim:

l. A reed relay unit comprising an elongated energizing coil, a layer of insulating material concentrically Within said coil, a copper enclosure within said insulating layer, and two elongated gas filled reed relay capsules substantially enclosed by said copper enclosure.

2. A reed relay capable of handling very small voltages without errors caused by temperature gradients comprising an elongated gas filled glass capsule having two ferromagnetic contact strips passing through it, a copper tube enclosing said capsule, an insulating layer surrounding 4 said copper tube, and an energizing coil around said insulating layer.

3. The relay unit of claim 1 `including at least one additional elongated reed relay capsule within said insulating layer but routside said copper enclosure.

4. An electrical reed relay unit capable of simultaneously Iachieving a plurality of electrical contacts without Vsigniicant temperature gradients within said unit lcomprising:

(a) an energizing coil; (b) an insulating layer within said energizing coil; (c) a plurality of reed relay capsules; and `(d) a thermal. shunt of a material selected from the Vgroup consisting of copper, copper alloys, and silver in having a high thermalrcouductivityiand high specific heat,

said shunt enclosing and extending at least to the extremities of said reeds;

(c) a layer of insulating material surrounding said thermal shunt; and

d an energizing coil over said insulating material approximately concentric with said thermal shunt.

No references cited. 

